A non-delivery report (NDR) is not a cause of email delivery issues, but does usually provide diagnostic information that helps with troubleshoot. Always read the NDR when one is available. Many issues reported in NDRs will be server-related.

One of the database issue is the dirty shutdown, When Exchange dismounts a database, the Information Store ensures that all transactions (dirty database pages) in cache are committed to the database (.edb) file. When this is allowed to happen, the database is said to be in “Clean Shutdown” and requires no transaction logs to mount because all transactions have already been replayed into the database.

When a user adds another user to their mailbox as a delegate, and chooses to have meeting requests sent to their delegates, a hidden inbox rule is created in their mailbox to perform the forwarding of those meeting requests. This can also apply to delegates room and equipment mailboxes.